A high-speed radio communication such as the radio LAN system is troubled by a problem that the transmission quality is degraded by the multipath fading or the shadowing, and this problem is serious indoors. A sector antenna has been investigated as one means for avoiding such degradation of transmission qualities. In this sector antenna, a plurality of antenna elements having principal beams directed in different directions are arranged and selectively switched according to the electric wave transmission environment.
Generally speaking, the antenna for a stationary station to be mounted in the ceiling or a terminal radio device a note personal computer used on a desk is required to have a planar constitution from the viewpoints of production or mobility. In the case of considering the indoor communication environments, on the other hand, the directivities of those antennas are desired such that the principal beam has an angle of elevation inclined (or tilted) from the vertical direction to the horizontal direction with respect to the antenna face. Considering the disposed position of the communication destination, moreover, it is desired that the tilting angle can be controlled.
As the sector antenna for realizing those radiation characteristics of tilting in the horizontal direction, there has been proposed a plane multi-sector antenna, which uses the “slot Yagi-Uda array”, as described in Non-Patent Document 1.
This multi-sector antenna is described with reference to FIG. 11. This multi-sector antenna has six slot arrays 102A to 1102F arrayed circularly in radial directions on a substrate 101, and each of these fix slot arrays 102A to 102F is composed of slots of five elements. In these slot arrays, the simplex characteristics are that the principal beam is formed with a vertical plane of an angle of elevation of 60 degrees, and that a conical plane has a half-value angle of about 56 degrees.
This multi-sector antenna is constituted such that a six-sector antenna having six sectors dividing the 360 degrees of the horizontal plane is formed arraying the six slot arrays at an interval of 60 degrees in the horizontal plane, and by feeding the individual slot arrays selectively. This sector antenna is so sized for an operating frequency of 5 GHz, for example, as to have a diameter L7 of 273 mm (or 4.55 wavelengths) and an area of 58,535 square mm.
Another antenna proposed is a multi-sector antenna using the “waveguide element sharing patch Yagi-Uda array”, as described in Patent Document 1.
This multi-sector antenna is described with reference to FIG. 12. This multi-sector is formed on the surface of a circular dielectric substrate 201 such that waveguide elements 203A to 203F of rectangular patches are arrayed radially around a regular hexagonal type waveguide element 202, and such that feeding elements 204A to 204F are arranged on the outer sides of the waveguide elements 203A to 203F. Thus, these three rows of waveguide elements intersect with each other at an angle of 60 degrees around the regular hexagonal type waveguide element 202, thereby to constitute the six-row patch Yagi-Uda array.
Here in case one feeding element is fed, the waveguide element row including the regular hexagonal type waveguide element operates as the Yagi-Uda array. At this time, the principal beam is formed in the direction of the vertical plane having the elevation angle θ of 45 degrees, and the conical plane pattern has a half-value angle of about 63 degrees. By thus feeding the feeding elements selectively, it is possible to constitute the six-sector antenna, in which the 360 degrees of the horizontal plane are divided by six. This sector antenna is sized for an operating frequency of 5 GHz, for example, to have a diameter L8 of 1.83 wavelength (110 mm) and an area of 9,503 square mm.
Non-Patent Publication 1: Papers (B) of Association of Electronic Information Communications, Vol. J85-B, No. 9, pp 1633-1643, September 2002.
Patent Document 1: JP-A-2003-142919.